Method of air separation into oxygen and argon

ABSTRACT

A method of air separation into oxygen and argon in double rectification columns with the drawing off of liquid or gaseous oxygen and simultaneous obtaining of argon by withdrawing a fraction of raw argon from one of the plates of the upper rectifying column, with a portion of the liquid oxygen flow being returned to said rectifying column onto a plate thereof that is located below the raw argon fraction withdrawal zone, whereby a forced circulation flow of liquid oxygen is created.

United States Patent [191 Balabaev et a1;

[ METHOD OF AIR SEPARATION INTO OXYGEN AND ARGON [76] Inventors: Georgy Matveevich Balabaev, ulitsa Shevchenko, 64-A, kv. 56; Vlktor Sergeevlch Boiko, 20106 1 Slobodskaya ulitsa, 9-A, kv. I3; Vlktor Matveevich Malchenko, 20109 ulitsa Spassky Spusk 20, korpus 7, kv. ll; Stepan Nikolaevlch Mlsarenko, ulitsa Novo-Sportivnaya, 65, kv. 81; Luvish Avrum-Abovich Tsitrin, ulitsa Krylova, l2, 4, kv. 25, all of Nikolaev; Evgeny lvanovich Borzenko, ulitsa Bukharestskaya, 3l, korpus 3, kv. I14; Georgy Anatollevlch Golovko, Pushkin, Bulvar A. Tolstogo, l6, kv. 129, both of Leningrad, all of U.S.S.R.

[22] Filed: July 15, 1971 [21] Appl. No.: 162,792

[52] U.S. Cl 62/29, 62/22, 62/41 [51] Int. Cl. F25j 3/02, F25j 3/03, F25j 3/08 [58] Field of Search 62/22, 41, 27, 28,

[451 Aug. 114, 11973 [56] References Cited UNITED STATES PATENTS 2,817,216 12/1957 Etienne 62/28 3,596,471 8/1971 Streich 62/22 2,547,177 4/1951 Simpsonm. 62/22 2,824,428 2/1958 Yendall. 62/29 3,127,260 3/1964 Smith 62/22 Primary ExaminerNorman Yudkoff Assistant Examiner-A. F. Purcell Att0rney-Eric H. Waters, John G. Schwartz et a1.

[5 7] ABSTRACT A method of air separation into oxygen and argon in double rectification columns with the drawing off of liquid or gaseous oxygen and simultaneous obtaining of argon by withdrawing a fraction of raw argon from one of the plates. of the upper rectifying column, with a portion of the liquid oxygen flow being returned to said rectifying column onto a plate thereof that is located below the raw argon fraction withdrawal zone, whereby a forced circulation flow of liquid oxygen is created.

1 Claim, 1 Drawing Figure METHOD OF AIR SEPARATION INTO OXYGEN ANDARGON The present invention relates to methods of producing oxygen, and more particularly to methods of air separation into oxygen and argon.

Known in the art is a method of air separation into oxygen and argon in double rectification columns, by drawing off liquid or gaseous oxygen and simultaneous production of argon by withdrawing a raw argon fraction from. one of the plates of the upper column.

The installation for carrying out said method, besides a double rectification column with. a condenser, comprises heat-exchange equipment, throttle valves, acetylene adsorbers, recoolers and a rectifying column for raw argon.

According to the known method, highly pressurized air purified from carbon dioxide, mechanical dust and dried upon leaving the main heat exchanger, is throttied to. a pressure of four to six atm and directed to the lower column. The air from the expander is also directed to the lower double rectification column, .where, as a result of rectification, still liquor is formed in the bottom portion of the column, containing 36-40 vol. percent of oxygen, and liquid nitrogen is collected in the pockets of the lower column, having a concentration of 98-99 vol. percent of nitrogen.

The still liquor is directed through the acetylene adsorber, expander and recooler into the middle portion of the upper column. Nitrogen from the pockets of the lower column is directed through the recooler and ex pander valve to the upper plate of the upper column. From the upper column, below the still liquor inlet, a fraction is withdrawn to be rectified in the raw argon column, the fraction having the following composition: 9 I 1 vol. percent of argon, about 0.5 percent of nitrogen, the rest being oxygen. From the upper portion of the raw argon column gaseous raw argon is drawn off that has the following composition: 90 92 vol. percent of argon, -4 vol. percent of nitrogen and 5-4 vol. percent of oxygen. The oxygen produced as a result of rectification, whose purity is 99.2-99.5 vol. percent, is accumulated in the condenser and is drawn off from the column in a liquid or gaseous state or, else, in a-liquid and partially gaseous state.

However, the known method is disadvantageous in that the purity of oxygen thus produced is not adequately high for ensuring cutting of metal without burrs.

The coefficient of obtaining raw argon is not sufficiently high either.

The argon fraction being withdrawn contains nitrogen which sharply deteriorates the rectification process in the raw argon column and is responsible for considerable losses of argon in the course of its further purification.

An object of the present invention is to provide a method of air separation into oxygen and argon which would ensure the production of oxygen with a purity as high as 99.9 vol. percent.

Another object of the invention is to increase the amount of raw argon obtained and to decrease the content of nitrogen therein.

In accordance with the said and other objects, the essence of the present invention resides in that in a method of air separation into oxygen and argon in double rectification columns with the drawing off of liquid or gaseous oxygen and simultaneous production of argon by withdrawing a fraction of raw argon from one of the plates of the upper column, a portion of the liquid oxygen flow is returned to the rectifying column onto its plate that is located below the raw argon fraction withdrawal zone, whereby a forced circulation flow of liquid oxygen is created.

This ensures the production of highly pure oxygen and an improvement in the quality of argon obtained.

Other objects and advantages of the present, invention will become more fully apparent from a consideration of the detailed description of an exemplary embodiment thereof in conjunction with the accompanying drawing which diagrammatically represents an installation for air separation into oxygen and argon by the method of the present invention.

Highly pressurized air after the main heat exchanger (not shown) having a temperature of from l40 to 1 50 C and pressure of 180 to 200 gauge atm. is throttled by a throttle valve 2 along a pipeline 1 and directed 'Lto a lower column 3.

After the throttling the temperature of the air is lowered to l to lC.

Air from the expander is also directed to the lower column 3 along a pipeline 4. As a result of primary rec tification, in pockets 5 of the lower column 3 liquid nitrogen is collected, which through a recooler 6 and a throttle valve 7 is directed to an upper column 8. The still liquor containing 36 to 40 vol. percent of oxygen from the still 9 of the lower column 3 through acetylene adsorbers l0 and a throttle valve 11 is supplied into the middle portion of the upper column 8. Oxygen that has collected in a condenser 12 is drawn off in a liquid state through a recooler 13, and a portion of oxygen is drawn off in a gaseous state along a pipeline 14 through a heat exchanger (not shown).

For producing highly pure oxygen (of the order of 99.9 vol. percent), into the bottom portion of the upper column 8 an oxygen circulation flow is introduced by feeding a portion of liquid oxygen that has been withdrawn after the recooler 13 or before it by a pump 15 into the upper column 8 onto one of its plates located below the argon fraction withdrawal zone.

The introduction of the oxygen circulation flow results in an increase of oxygen concentration in the place of such introduction, better rectification conditions are created on the bottom plates of the upper rectifying column 8 and the concentration of oxygen in the liquid of the condenser 12 is increased to about 99.9 vol. percent. At the same time the content of nitrogen is brought down to 0.1 vol. percent in the argon fraction withdrawn from the upper column 8 in the form of vapors along a pipeline 16; better conditions are created for rectification in a raw argon column 17, since the fraction composition then closer approximates a binary mixture, so that the yield of raw argon is increased and the quality thereof becomes higher. The high-quality raw argon (97.5 to 98.0 vol. percent of argon, 0.2 to 0.5 vol. percent,"of nitrogen, the rest being oxygen) is withdrawn from the raw argon column 17 in a gaseous state along a pipeline l8, and the downflowing liquid phlegm is returned to the upper column 8 along a pipeline l9.

Condenser 20 of the raw argon column 17 is fed with the still liquor.

Nitrogen is removed from the upper column 8 along a pipeline 21 through the recoolers 6 and 13 and other rectifying column with the drawing off of liquid or gaseous oxygen; simultaneously withdrawing a fraction of raw argon from an upper section of said rectifying columnand returning a portion of the flow of liquid oxygen to the rectifying column at a point below the raw argon fraction withdrawal zone, a forced circulation flow of liquid oxygen being thus created. 

